Optical multiplexers/optical demultiplexers are essential devices in optical integrated circuits and communication optical modules. Heretofore, various structures and manufacturing methods have been proposed. Examples are as follows:
[Patent Document 1] Japanese Unexamined Patent Application Publication No. 2005-157091
[Patent Document 2] Japanese Unexamined Patent Application Publication No. 2005-189385
[Patent Document 3] Japanese Unexamined Patent Application Publication No. 2003-207669
[Patent Document 4] Japanese Patent No. 3500962
[Non-patent Document 1] Appl. Opt., vol. 40, No. 32, pp. 5860-5871 (2001)
Patent Documents 1 and 2 disclose techniques for forming a branching waveguide by photolithography. According to these techniques, a photosensitive polymeric material is used to form a branching pattern by exposure technology, such as photolithography. Patent Document 3 discloses a technique for forming an optical waveguide by curing a resin in a groove. In this technique, an optical waveguide is formed by curing a resin in a groove having a branching pattern formed in a mold, for example, by stamping, embossing, or imprinting. Patent Document 4, which was filed by the present inventors, discloses a manufacturing method in which a half-mirror is previously disposed along the growth direction of a self-written waveguide to cause the waveguide to branch off. The term “self-written”, as used herein, means that, in the curing of a photocurable resin by curing light, a cured portion serves as a core to confine the curing light because of a difference in refractive index between the cured portion and an uncured portion, thus forming an optical waveguide as the core self-grows forward. The details can also be found in other patent documents filed by the present inventors. Non-patent Document 1 reports that a self-written optical waveguide having a plurality of tips depending on the mode order can be formed by adding a photocurable resin dropwise on one end face of an optical fiber facing upward and exciting an LP11 mode or an LP21 mode in the optical fiber by inputting a light from the other end face of it.